(1) Field of the Invention
The present invention relates to the transport of crane booms and particularly to maintaining the movements of a boom being transported from one construction site to another within safe limits. More specifically, this invention is directed to apparatus for causing an extended boom element to move in tandem with a carrier vehicle and especially to a boom support assembly which may be detachably connected to a crane boom to provide support for the end thereof disposed away from the carrier vehicle. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
There are numerous problems associated with the transportation of extended crane booms. These problems include possible damage to the pendant cables, which are used to support the boom during transport, resulting from the stresses applied thereto as a result of the bouncing action produced by uneven terrain. This bouncing action, which is probably aggravated by the springing action of the pendant cables, tends to unbalance the moving crane and may cause damage to the road surface or overhead objects. Also, there is considerable wear to the crane turntable resulting from bounce and the unbalancing of the load resulting therefrom. Further, prior art techniques of transporting a crane boom typically impose extra weight on the rear axles of the transport vehicle causing excess tire wear and wear to mechanical components. As a result of the extra weight on the rear axles, the transport vehicle is often subjected to "over-light" steering due to the unloading of the front axles thereof and this "over-light" steering may result in a dangerous lack of control. Stiff-legged transport, wherein tension is applied to the pendant cables to suspend the boom roughly parallel to the road surface, produces severe complications in negotiating corners since the boom remains straight behind the transport vehicle and thus may damage surrounding property. Also in "stiff-legged" transport, extreme stresses are imposed on the swing lock which holds the boom/crane system straight behind the carrier. All of the above problems result in the necessity of disassembling the boom and shipping it separately when regulations prohibit stiff-legged transport or where clearances preclude the use of stiff-legged transport to move the boom to the desired site.
Prior attempts to overcome the above-discussed problems are exemplified by the devices shown in U.S. Pat. Nos. 3,747,957 and 3,224,597. U.S. Pat. No. 3,747,957 discloses a trailer having a generally triangular configuration with an axle positioned at one corner and the other corners respectively being attached to the carrier vehicle and boom. The technique of U.S. Pat. No. 3,747,957 suffers the disadvantages that different size trailers must be provided for different length booms and a special trailer hitch must be provided to attach the trailer to the carrier vehicle.
U.S. Pat. No. 3,224,597 discloses a double axle support assembly which is attached to the carrier vehicle by means of a tongue. As in the case of the technique of U.S. Pat. No. 3,747,957, the carrier vehicle must be provided with a compatible trailer hitch. Further, the technique of U.S. Pat. No. 3,224,597 contemplates the interconnection of the support with the crane cab on the carrier vehicle by means of a complex arrangement of cables and thus the technique is time consuming and difficult to implement.